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Equipment Discussions >> Reflectors

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jonstarrysky
professor emeritus


Reged: 01/03/09

Loc: England, U.K.
f/4 or faster dobs: favourite widefield eyepiece? new
      #5689617 - 02/19/13 08:03 PM

Folk who actually use f/4 or faster dobs: what is your favourite eyepiece for max field of view ?
We will assume Paracor is being used, which will turn f/4 into f/4.6. Televue will say to avoid exit pupils of >7mm for newtonians. This means that the 31mm Nagler is just about OK on an f/4 dob. Dogma says that the 26mm Nagler or 21mm Ethos is more suitable, generating a better exit pupil. But at the end of the day the 31mm Nagler will give the widest views, especially since the Ethos has much of the field in peripheral vision. It would seem that the 31mm Nagler is popular with owners of fast dobs, indicating that in practise the exit pupil dogma maybe doesnt matter so much.....


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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: f/4 or faster dobs: favourite widefield eyepiece? new [Re: jonstarrysky]
      #5689661 - 02/19/13 08:22 PM

Quote:

Folk who actually use f/4 or faster dobs: what is your favourite eyepiece for max field of view ?
We will assume Paracor is being used, which will turn f/4 into f/4.6. Televue will say to avoid exit pupils of >7mm for newtonians. This means that the 31mm Nagler is just about OK on an f/4 dob. Dogma says that the 26mm Nagler or 21mm Ethos is more suitable, generating a better exit pupil. But at the end of the day the 31mm Nagler will give the widest views, especially since the Ethos has much of the field in peripheral vision. It would seem that the 31mm Nagler is popular with owners of fast dobs, indicating that in practise the exit pupil dogma maybe doesnt matter so much.....




I love 31mm Nagler in my 12.5 inch F/4.06. I use it with a Paracorr. I recently measured my exit pupil, seems to be just about 7mm... if I can keep my eyes open that is.

Jon


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cloudmagnet
sage


Reged: 12/04/08

Loc: Georgetown, Texas
Re: f/4 or faster dobs: favourite widefield eyepiece? new [Re: Jon Isaacs]
      #5689680 - 02/19/13 08:36 PM

Ditto what Jon said- mine is a 14" f/4.8, but the 31mm Nagler with Paracor have practically taken roots in my focuser!

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hbanich
Pooh-Bah
*****

Reged: 06/17/05

Loc: Portland, Oregon
Re: f/4 or faster dobs: favourite widefield eyepiece? new [Re: Jon Isaacs]
      #5689687 - 02/19/13 08:39 PM

I prefer the 21 Ethos with my 28 inch f/4 and 8 inch f/4 Newtonians. Although the 31 Nagler gives a wider fov the increased magnification of the Ethos more than makes up for it. Plus it makes it easier to see fainter details.

However, I'm intrigued by the 25mm ES and hope to have a look through one to see if I change my mind…


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turtle86
Pooh-Bah Everywhere Else
*****

Reged: 10/09/06

Re: f/4 or faster dobs: favourite widefield eyepiece? new [Re: jonstarrysky]
      #5689693 - 02/19/13 08:43 PM

Quote:

Folk who actually use f/4 or faster dobs: what is your favourite eyepiece for max field of view ?
We will assume Paracor is being used, which will turn f/4 into f/4.6. Televue will say to avoid exit pupils of >7mm for newtonians. This means that the 31mm Nagler is just about OK on an f/4 dob. Dogma says that the 26mm Nagler or 21mm Ethos is more suitable, generating a better exit pupil. But at the end of the day the 31mm Nagler will give the widest views, especially since the Ethos has much of the field in peripheral vision. It would seem that the 31mm Nagler is popular with owners of fast dobs, indicating that in practise the exit pupil dogma maybe doesnt matter so much.....




I think you've pretty much answered your own question. My Dob is actually an f/4.3 but I don't think my answer would be any different if my scope were f/4--as much as I like my 21mm Ethos for most wide-field situations, I still find my 31mm Nagler very useful when I want the widest possible TFOV with the largest DSO's. Plus, I've found that the larger (and brighter) exit pupil of the 31mm Nagler will let me see faint DSO's like the Horsehead and California Nebulas when the smaller exit pupil of the 21mm Ethos won't.


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jonstarrysky
professor emeritus


Reged: 01/03/09

Loc: England, U.K.
Re: f/4 or faster dobs: favourite widefield eyepiece? new [Re: hbanich]
      #5689700 - 02/19/13 08:49 PM

To elaborate on my original post. I currently have Naglers 26mm & 20mm and Ethos 21mm. Kind of a strange mix, the 21mm Ethos is more or less the same as the 26mm Nagler in TFOV, and more or less the same magnification as the 20T5. I'm considering culling the 21E and buying the 31N to make a Nagler triplet: 31,26,20. Main scope is 10" f/4.7 but I am about to start using an 18" f/4.

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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: f/4 or faster dobs: favourite widefield eyepiece? new [Re: jonstarrysky]
      #5689716 - 02/19/13 09:01 PM

Just to clarify... I think the 31mm Nagler is fine for scopes F/4 or slower when used with a Paracorr.

When you start getting much below F/4, the 21mm Ethos seems to be a better choice.

Jon


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Aquatone
sage


Reged: 03/23/06

Loc: Moraga, CA (Bay Area)
Re: f/4 or faster dobs: favourite widefield eyepiece? new [Re: Jon Isaacs]
      #5690053 - 02/20/13 12:43 AM

The 21mm Ethos is perfect in my F/3.25 24" with Paracorr 2... but I will confess that sometimes (nervously watching over my shoulder just in case the exit pupil police are checking up) I furtively slide in a 31mm T5. I am a habitual offender I know, but the view is really worth the risk and penalties.

Chris


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jonstarrysky
professor emeritus


Reged: 01/03/09

Loc: England, U.K.
Re: f/4 or faster dobs: favourite widefield eyepiece? new [Re: Aquatone]
      #5690172 - 02/20/13 04:00 AM

Quote:

The 21mm Ethos is perfect in my F/3.25 24" with Paracorr 2... but I will confess that sometimes (nervously watching over my shoulder just in case the exit pupil police are checking up) I furtively slide in a 31mm T5. I am a habitual offender I know, but the view is really worth the risk and penalties.

Chris




lol I guess this hits the nail on the head, the 31Nagler is supposed to be non-ideal for a fast scope, but 1st hand experience of what it actually delivers is what matters. What got me thinking was Webster Telescopes - their standard scopes are all f/4 or faster. But look at pictures of their scopes, and read their user instructions etc, when you see something in the focusser, it will be the 31 Nagler.

I guess another logical way forward for me would be 31mm Nagler, 21mm Ethos and to cull my 20 and 26mm Naglers. But these Naglers are really comfortable eyepieces to use, easy to look through for long periods, eye positioning is very easy. Looking through the Ethos perhaps requires more effort, even though the wow factor is obvioulsy greater...


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Jon Isaacs
Postmaster
*****

Reged: 06/16/04

Loc: San Diego and Boulevard, CA
Re: f/4 or faster dobs: favourite widefield eyepiece? new [Re: jonstarrysky]
      #5690193 - 02/20/13 05:02 AM

Quote:

Quote:

The 21mm Ethos is perfect in my F/3.25 24" with Paracorr 2... but I will confess that sometimes (nervously watching over my shoulder just in case the exit pupil police are checking up) I furtively slide in a 31mm T5. I am a habitual offender I know, but the view is really worth the risk and penalties.

Chris




lol I guess this hits the nail on the head, the 31Nagler is supposed to be non-ideal for a fast scope, but 1st hand experience of what it actually delivers is what matters. What got me thinking was Webster Telescopes - their standard scopes are all f/4 or faster. But look at pictures of their scopes, and read their user instructions etc, when you see something in the focusser, it will be the 31 Nagler.

I guess another logical way forward for me would be 31mm Nagler, 21mm Ethos and to cull my 20 and 26mm Naglers. But these Naglers are really comfortable eyepieces to use, easy to look through for long periods, eye positioning is very easy. Looking through the Ethos perhaps requires more effort, even though the wow factor is obvioulsy greater...




There is a lot of difference between F/3.25 and F/4 when it comes to the 31mm Nagler. Both pretty much require Paracorr and at F/4, you are at F/4.6 with the Paracorr which makes the 31mm Nagler a reasonable choice. At F/3.25 you are working at F/3.74 and a 8.3 mm exit pupil, not so bad if your eye opens reasonably wide but if it only opens to 5mm, then the 21mm Ethos makes more sense.

You're at F/4 with presumably a Paracorr so the 31mm is fine.

Jon


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Mike Lockwood
Vendor, Lockwood Custom Optics
*****

Reged: 10/01/07

Loc: Usually in my optical shop
Re: f/4 or faster dobs: favourite widefield eyepiece? new [Re: turtle86]
      #5690678 - 02/20/13 11:30 AM

Quote:

Plus, I've found that the larger (and brighter) exit pupil of the 31mm Nagler will let me see faint DSO's like the Horsehead and California Nebulas when the smaller exit pupil of the 21mm Ethos won't.



Your scope is f/4.3.

Below f/4, for me, I find the opposite to be true. I find that the 21mm Ethos shows objects brighter. The exit pupil of the 31mm is just too big for my eye at f/3.6 or f/3.3, and I can notice the difference in lost light. Also, the Ethos are better near the edge of the field.

Of course a Paracorr 2 is always used, so the real f# is 15% higher. (I'm not a fanatic about dark adaptation, by the way, so I could probably get my pupils more dilated if I tried.)

I still occasionally use the 31mm or 41mm Panoptic for fun, though, to fit really large optics like the Rosette in the field of view. Yes, it's like stopping down the scope, but then again that means you don't have to bring along another smaller scope for wide field views. Besides, the telescope police rarely give tickets for exit pupil violations.


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alancygnusx2
professor emeritus


Reged: 11/25/08

Loc: CA
Re: f/4 or faster dobs: favourite widefield eyepiece? new [Re: jonstarrysky]
      #5690830 - 02/20/13 12:52 PM

In my 24 3.3 I find the 21Ethos is my favorite, but for moments where a slighly wider field is desired the 31 nagler goes in.

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turtle86
Pooh-Bah Everywhere Else
*****

Reged: 10/09/06

Re: f/4 or faster dobs: favourite widefield eyepiece? [Re: Mike Lockwood]
      #5690862 - 02/20/13 01:09 PM

Quote:

Quote:

Plus, I've found that the larger (and brighter) exit pupil of the 31mm Nagler will let me see faint DSO's like the Horsehead and California Nebulas when the smaller exit pupil of the 21mm Ethos won't.



Your scope is f/4.3.

Below f/4, for me, I find the opposite to be true. I find that the 21mm Ethos shows objects brighter. The exit pupil of the 31mm is just too big for my eye at f/3.6 or f/3.3, and I can notice the difference in lost light. Also, the Ethos are better near the edge of the field.

Of course a Paracorr 2 is always used, so the real f# is 15% higher. (I'm not a fanatic about dark adaptation, by the way, so I could probably get my pupils more dilated if I tried.)

I still occasionally use the 31mm or 41mm Panoptic for fun, though, to fit really large optics like the Rosette in the field of view. Yes, it's like stopping down the scope, but then again that means you don't have to bring along another smaller scope for wide field views. Besides, the telescope police rarely give tickets for exit pupil violations.




Obviously lots of variables at play here--focal ratio of the scope, how dark the observing site is, the viewing conditions, how wide the observer's pupils can dilate, and so on. Even with my f/4.3 scope I generally prefer the 21mm Ethos over the 31mm Nagler for widefield, and also find that many objects appear brighter and with more contrast with the 21mm Ethos. But I've also found that on some occasions I could see the Horsehead only with the 31mm Nagler, and not with the 21mm Ethos.

I actually used to enjoy using a 40mm Paragon with my scope before upgrading to a 31mm Nagler. Despite the massive exit pupil of over 9mm without a Paracorr (about the same as a 31mm Nagler in an f/3 system with a Paracorr), large, bright DSO's like the Double Cluster and Andromeda still made for excellent eye candy. I knew I was giving up some photons, but in those situations I found it worthwhile to gain the extra TFOV. The 31mm Nagler is better, of course, due to the smaller exit pupil. I've never gotten a ticket from the exit pupil police at star parties, though more than once I've been let off with a warning.


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